Corrosion-resistant alloy

ABSTRACT

Corrosion-resisting alloy useful for molding surface formed of the alloy for molding of resin, the alloy including nickel, copper andberyllium in certain ranges of proportions.

United States Patent 1191 Karlyn Feb. 5, 1974 CORROSlON-RESISTANT ALLOY1,685,570 9/1928 Masing et a1. 75/170 x Inventor: David A. y y, Mass3,437,480 4/1969 Cape 75/170 [73] Ass1gnee: USM Corporatlon, Boston,Mass. Primary G g T. Ozaki [22] Filed: Dec. 16, 1971 Attorney, Agent, orFirmRichard B. Me'gley et a1.

[21] Appl, No.: 208,884

52 us. (:1. 75/170, 249/135 [57] ABSTRACT [51] Int. Cl. CZZC 19/00Corrosiomresisting alloy useful for molding Surface [58] Field of Search75/170 formed of the alloy for molding of resin, the alloy i I cludinnickel, co er andber Ilium in certain ran es [56] References Clted ofprolgaortionsv pp y g UNITED STATES PATENTS 1,974,060 9/1934 Cooper75/170 2 Claims, No Drawings '1 CORROSION-RESISTANT ALLOY BACKGROUND OFTHE INVENTION This invention relates to an alloy resistant to corrosionparticularly under conditions encountered in molding expanded resin.

The manufacture of articles of plastic by filling a mold with a fluidmass of plastic and solidifying it is an increasingly important processfor making a variety of useful or ornamental articles includingfurniture components, cabinets, cases and other articles. A majorelement ofthe cost of molding plastic articles is the provision ofsuitable molds. The mold surface determines the shape surface characterand finish of the molded article so that mechanical shaping of a moldingsurface requires the work of skilled craftsmen and is very costly. Moldshave been formed by casting molten metal around a master and a berylliumcopper alloy has been found outstanding in its ability to reproduce finesurface detail such, for example, wood grains.

While such cast molds have been found useful in various relations,.ithas been found that severe corrosion problems develop in the use of suchmolds for expanded plastic articles.

It is an object of the present invention to provide an alloy resistantto corrosion in the molding of expanded plastic articles.

SUMMARY OF THE INVENTION To these ends and according to a feature of thepresent invention, I have provided a ternary alloy of nickel, copper andberyllium in crtain ranges of proportions useful for forming a corrosionresisting molding surface.

PREFERRED EMBODIMENT I have found a series of alloys of nickel, copperand beryllium, which are highly resistant to corrosive agents generatedat surfaces of molds for plastics and which possess outstanding abilityto reproduce fine surface detail of a master against which molten alloyis cast. Molds formed of the alloy also possess hardness, machineabilityand other physical properties providing outstanding performance in use.The special combination of properties is secured in'ternary alloyscomprising, based on 100 parts by weight of alloy from about 50 to about80 parts by weight of nickel, from about 50 to about parts by weightofcopper and from about one to about three parts by weight of beryllium.

Preferred ternary alloys will come in the range of from about 55 toabout 65 parts by weight of nickel,

from about to about parts by weight of copper and from about 1.5to'about 2.5 parts by weight of beryllium with a hardness of about 20 orhigher on the Rockwell C Scale.

The alloys of this invention may be made conveniently be meltingtogether an alloy of copper and beryllium with either nickel or an alloyof nickel and beryllium in proportions to give the above ternary alloysin the ranges of composition set forth above. Conventional melting andmixing procedures have been found satisfactory for preparing thesealloys.

Manufacture of molds by casting may involve preparing a model of thearticle to be molded or using a prototype of the desired article as amodel, and casting a commercially available self-curing rubber-typemolding material, such as a silicone rubber, around the model and curingit. The cured rubber molding materialvis stripped from the model andused for casting a refractory molding material which will form at leasta part of a mold for casting the alloy. Suitable materials for forming arefractory mold are compositions comprising a dispersion of a suitablerefractory powder in solution of a binder such as ethyl silicate in avolatile solvent such as alcohol. Suitable materials and procedures forthe refractory, mold forming are those described, for example, in theU.S. Pat. to Shaw No. 2,795,022 entitled Method of Making Molds, whichissued June ll, 1957.

After the refractory molding material has been formed into the rubbermold, it is caused to set, the mold is stripped away and the refractorymaterial is then baked, preferably after a primary firing step to give asurface porosity to form a smooth porous mold for casting the moltenalloy.

Casting of the alloy involves melting it by heat, preferably in aninduction furnace from a temperature which may be about 2,400 to 2,600F. and pouring the molten material into the refractory mold where itsolidifies. The refractory mold is then removed from the casting and thecasting may be air-cooled or quenched in oil at room temperature. Thealloy casting in this condition reproduces accurately the fine detail ofthe refractory mold surface and has strength and hardnes fitting it foruse as a mold part for molding plastics. The casting may be subjected tofurther heat treatments if desired but such further treatment is notnecessary. Molds cast of the alloy are readily machined I and drilledfor cooperation with other mold parts and with plastic injection moldingmachines.

The mold may be used with injection molding apparatus and processes ingeneral, but is particularly useful for the molding of foamedthermoplastic articles because of its resistance to ammonia or othernitrogenous gases generated by chemical foaming agents such as azodicarbonamide and p-toluene sulfonyl semicarbazide and other blowingagents used in such processes. Molding processes involve forming aheated mass of thermoplastic material which, in the case of foamedplastic molding will also include a blowing agent, in an injectionmolding machine, for example, a reciprocally movable screw-typeinjection molding machine, and operating the machine to force themixture into the mold where the blowing agent, if such is employed,releases gas to expand the thermoplastic material to fill the mold.After expansion of the thermoplastic material, the thermoplasticmaterial is hardened by cooling, and thereafter removed from the mold.Molds formed of the new alloyshave been found to provide good hardness,strength and thermal conductivity properties and withstand extended usein the making of molded articles including thermoplastic foamed articleswithout objectionable corrosion or wear.

The following example is given to aid in understading the invention andit is tobe understood that the invention is not restricted to theparticular materials, procedures or conditions employed in the example.

EXAMPLE I perature of about 2,400 F. for 5 minutes.

3. The molten alloy thus prepared was poured into a refractory moldformed by the steps of casting a cured silicone rubber form around a bedsplat and casting refractory material in the cured silicone rubber form,drying and baking the refractory. When the molten alloy had solidified,the refractory mold was broken away and the resulting cast alloy wascooled in air.

The sprue was removed and edge surfaces of the casting material weremachined for mating cooperation with a closure member for forming a moldfor molding of plastic bed splats. After machining of the matingsurface, appropriate mounting and cooling channels were formed in themold. No difficulty in machining or drilling was encountered.

' The mold was brought to a temperature of about 40 F., positioned inoperative relation to an injection molding machine and the moldingmachine was operated to injection mold an impart polystyrene moldingcomposition.

The injection molding composition was an impact polystyrene having aspecific gravity of 1.05 and a melting point as determined by the VicatTest (ASTM D-569) of about 220 F., the polystyrene being in pellet formand being dusted with about 0.5 percent by weight based on the weight ofthe polystyrene of azo dicarbonamide blowing agent. The pellets weresupplied to a reciprocally movable screw-type injection molding machinewith its barrel temperature set at 370 F., and with a pressure of 980psi. At this temperature and pressure the polystyrene was reduced tomolten condition without significant foaming and was injected into themold where it expanded to fill a mold cavity at 40 F. in an injectiontime of seconds. The molded polystyrene was removed from the mold afterabout 90 seconds.

The injection molding machine was operated in production of more than5,000 plastic molded bed splats and no corrosion of the molding surfacewas observed. The surface of the molded articles was a substantiallyexact replica of the surface of the mold splat used as the model withexcellent reproduction of fine detail including detail at the joints ofthe components making up the model bed splat..

EXAMPLE II A series of alloys was prepared having the followingcompositions, the percentages being percent by weight:

The above alloys were subjected to a spiral fluidity test comparable tothe tests described on Page 200 in connection with FIG. 3 of theAmerican Society for Metals Handbook, 1948 Edition, published by theAmerican Society for Metals, Metals Park, Ohio. The testv involvedpouring the molten material into a ceramic mold, providing a spiralchannel of roughly semicircular section one-quarter inch across the baseand three-sixteenths inch from the base to the top of the curve. Thetotal spiral length of the channel was 55 inches and the spiral wascontained in an area about 12 inches X12 inches.

Alloy A progressed only 2 inches along the spiral channel while AlloysB, C, and D traveled 7 inches, 12 inches and 20 inches around thechannel. Alloy E, which is the well-known Cu 2 Be, traveled 25 inches.

EXAMPLE 111 Fine turnings were prepared from Alloys A through E ofExample [I and these turnings were subjected to an accelerated corrosiontest as outlined below.

Weighed amounts of the turnings were placed in a beaker along withconcentrated ammonia solution (29 percent by weight ammonia) containing0.3 percent hydrogen peroxide. The beakers containing the turnings andsolution were kept for 5 days in a closed chamber in which an ammoniaatmosphere was maintained. Thereafter, the beakers were removed, theturnings were washed with distilled water, rinsed with ethyl alcohol anddried for 30 minutes at 65 C. The dried turnings were then weighed andthe loss of weight determined. v

It was foundthat the loss of weight in Alloys A, B, C and Dwasnegligible, in all cases being less than 0.2 percent. On the other hand,Alloy E, the known Alloy Cu 2 Be, has lost over 15 percent of its weightor times the weight lost by the other alloys. This test, whilequalitative only, has been found to coincide with the rate of corrosionof the alloy in use in molds for the molding of expanded plasticmaterial involving the use of blowing agents such as azo (bis)dicarbonamide and other blowing agents which evolve ammonia or othernitrogenous gases.

Having thus described my invention what I claim as new and desire tosecure by Letters Patentof the United States is: t

l. A ternary alloy resistant to surface corrosion by.

weight of beryllium.

2. A ternary alloy as defined in claim 1 comprising from 55 to 65 partsby weight of nickel, from 35 to 45 parts by weight of copper and from1.5 to 2.5 parts by weight of beryllium.